Metoprolol is a beta1-selective (cardioselective) adrenoceptor blocking agent. It is commercially available in two salt forms; one of them is tartrate salt available as Lopressor tablets and the other is succinate salt (Formula I) available as Toprol-XL tablets. Metoprolol is chemically, (±) 1-(isopropylamino)-3-[p-(2-methoxyethyl) phenoxy]-2-propanol. Metoprolol succinate is indicated in the treatment of hypertension, angina pectoris and heart failure.

U.S. Pat. Nos. 4,927,640 and 4,957,745 disclose a controlled release preparation containing a number of beads comprising insoluble cores coated with metoprolol. The beads have a high content of metoprolol in the range of 95-100% w/w of the soluble part of the bead. Insoluble cores, such as glass and silicon dioxide are used.
U.S. Pat. No. 5,001,161 discloses a pharmaceutical composition comprising metoprolol succinate together with a sustained release pharmaceutically acceptable carrier.
U.S. Patent Publication 20030185887 discloses a controlled or sustained release dosage formulation of propranolol where the inert core is coated with a solution of propranolol, water insoluble binder and filler. The active core so produced is further coated with a release-controlling layer.
U.S. Patent Publication 20050008701 discloses a controlled release pellet comprising water-soluble or water swellable inert core and a drug layer applied to it, along with a controlled release coating surrounding the drug layer.
International (PCT) Publication WO2005084636 discloses an oral controlled-release pharmaceutical composition of metoprolol succinate comprising a water-soluble, water swellable or water-insoluble inert core; one or more drug layers comprising metoprolol and one or more polymeric coatings surrounding the one or more drug layers. The water-soluble inert core comprises sugar sphere or salt, water insoluble inert core comprises silicon dioxide, small particles of glass, plastic resin particles or mixtures thereof and water swellable inert core comprises hydroxypropyl methylcellulose, microcrystalline cellulose, starch or mixture thereof.
Several other controlled release/extended release pharmaceutical compositions are known for example, in U.S. Pat. Nos. 5,399,362; 5,399,358; 5,707,656; 5,709,882; and 4,871,549; U.S. Application Nos. 20020177579; 20050266078; 20060003007; and 20040228915.